King's College London

Research portal

Specific absorption rate and temperature in neonate models resulting from exposure to a 7T head coil

Research output: Contribution to journalArticlepeer-review

Shaihan J. Malik, Jeffrey W. Hand, Ryan Satnarine, Anthony N. Price, Joseph V. Hajnal

Original languageEnglish
Pages (from-to)1299-1313
Number of pages15
JournalMagnetic resonance in medicine
Volume86
Issue number3
Early online date3 Apr 2021
DOIs
Accepted/In press6 Mar 2021
E-pub ahead of print3 Apr 2021
PublishedSep 2021

Bibliographical note

Funding Information: ERC (319456 [dHCP project]), the Wellcome EPSRC Center for Medical Engineering at King?s College London (WT 203148/Z/16/Z), and the National Institute for Health Research Biomedical Research Center based at Guy?s and St. Thomas? National Health Service Foundation Trust and King?s College London The authors acknowledge the receipt of scientific licenses for Sim4Life from Zurich MedTech (www.zurichmedtech.com) and support from the National Institute for Health Research (NIHR) Biomedical Research Centre based at Guy?s and St Thomas? NHS Foundation Trust and King?s College London. The views expressed are those of the authors and not necessarily those of the NHS, the NIHR or the Department of Health. Publisher Copyright: © 2021 International Society for Magnetic Resonance in Medicine Copyright: Copyright 2021 Elsevier B.V., All rights reserved.

King's Authors

Abstract

Purpose
To investigate safe limits for neonatal imaging using a 7T head coil, including both SAR and temperature predictions.
Methods
Head-centered neonate models were simulated using finite-difference time-domain based electromagnetic and thermal solvers. The effects of higher water content of neonatal tissues compared to adults, position shifts, and thermal insulation were also considered. An adult model was simulated for comparison.
Results
Maximum and average SAR are both elevated in the neonate when compared with an adult model. When normalised to B1+ the SAR experienced by a neonate is greater than an adult by approximately a factor two; when normalised to net forward power (forward-reflected) this increases to a factor of 2.5-3; and when normalised to absorbed power, approximately a factor of four. Use of age-adjusted dielectric properties significantly increases the predicted SAR, compared with using adult tissue properties for the neonates. Thermal simulations predict that change in core temperature/maximum temperature remain compliant with IEC limits when a thermally insulated neonate is exposed at the SAR limit for up to an hour.
Conclusion
This study of two neonate models cannot quantify the variability expected within a larger population. Likewise the use of age-adjusted dielectric properties has a significant effect, but while their use is well motivated by literature, there is uncertainty in the true dielectric properties of neonatal tissue. Nevertheless, the main finding is that unlike at lower field strengths, operational limits for 7T neonatal MRI using an adult head coil should be more conservative than limits for use on adults.

View graph of relations

© 2020 King's College London | Strand | London WC2R 2LS | England | United Kingdom | Tel +44 (0)20 7836 5454